I was mistaken, port 0xFC is always active high. I confirmed it by setting
the cocktail switch bit on Space Fury and sure enough, the second control
panel bits appeared in the self test.. all active because I flipped the
sense of them in the simulated input port. I've corrected version 1.6 of
the document. I didn't bump the rev number since I figured noone has had
a chance to pick up a copy yet...
